The purpose of this protocol is to evaluate the differential uptake of the glucose analog, FDG, in tumor and brain in the awake human compared to the uptake while the same subject is under barbiturate anesthesia. It is our hypothesis that when neuronal activity is suppressed the ratio of FDG uptake between tumor and brain will be increased. If this proves to be so it implies that cytotoxic glucose analogs may be useful in the treatment of malignant brain tumors by taking advantage of the decreased uptake of the agent in the metabolically suppressed brain compared to the tumor. Barbiturate suppression of neuronal cerebral metabolic activity may also prove useful in detecting lesions which are not synaptically active and are not detected with more conventional imaging techniques.